EMC2104 Datasheet, PDF (97/101 Pages) SMSC Corporation – Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown

Dual RPM-Based PWM Fan Controller with Hardware Thermal Shutdown
Datasheet
Appendix C RPM to Tachometer Count Look Up Table
C.1
1k RPM Range
The Look Up Table is an example based on the assumption that the fan being measured has 2-poles
and is measuring 5 edges using the 1k RPM range settings. The data presented in the reading is only
the high byte data and the decimal count value only represents high byte data.
Table C.1 Tachometer Count to RPM Look Up Table (Range = 1000 RPM)
TACH COUNT
(DECIMAL)
0
32
64
96
128
160
192
224
256
288
320
352
384
416
448
480
512
544
576
608
640
672
704
736
768
REGISTER
READING (HEX)
00
01
02
03
04
05
06
07
08
09
0A
0B
0C
0D
0E
0F
10
11
12
13
14
15
16
17
18
FAN SPEED
(RPM)
Disabled
245760
122880
81920
61440
49152
40960
35109
30720
27307
24576
22342
20480
18905
17554
16384
15360
14456
13653
12935
12288
11703
11171
10685
10240
TACH COUNT
(DECIMAL)
4096
4128
4160
4192
4224
4256
4288
4320
4352
4384
4416
4448
4480
4512
4544
4576
4608
4640
4672
4704
4736
4768
4800
4832
4864
REGISTER
READING
(HEX)
80
81
82
83
84
85
86
87
88
89
8A
8B
8C
8D
8E
8F
90
91
92
93
94
95
96
97
98
FAN SPEED
(RPM)
1920
1905
1890
1876
1862
1848
1834
1820
1807
1794
1781
1768
1755
1743
1731
1719
1707
1695
1683
1672
1661
1649
1638
1628
1617
SMSC EMC2104
97
DATASHEET
Revision 1.74 (05-08-08)